Motivated Multitasking: How the Brain Keeps Tabs on Two Tasks at Once

New research shows that rather than being totally devoted to one goal at a time, the human brain can distribute two goals to different hemispheres to keep them both in mind--if it perceives a worthy reward for doing so

The human brain is considered to be pretty quick, but it lacks many of qualities of a super-efficient computer. For instance, we have trouble switching between tasks and cannot seem to actually do more than one thing at a time. So despite the increasing options—and demands—to multitask, our brains seem to have trouble keeping tabs on many activities at once.

A new study, however, illustrates how the brain can simultaneously keep track of two separate goals, even while it is busy performing a task related to one of the aims, hinting that the mind might be better at multitasking than previously thought.

"This is the first time we observe in the brain concurrent representations of distinct rewards," Etienne Koechlin, director of the cognitive neuroscience laboratory at the French National Institute for Health and Medical Research (Inserm) in Paris and coauthor of the new study, wrote in an email to ScientificAmerican.com.

For the study, 32 right-handed subjects were asked to match letters while their brain activity was recorded with functional magnetic resonance imaging (fMRI). Subjects were motivated by a monetary reward they would receive based on how many letters they matched without error. During this baseline test, both hemispheres of the brain's medial frontal cortex (which is involved in motivation) appeared active. However, when the researchers introduced a second task, where the subjects had to match like uppercase letters in addition to matching like lowercase letters with separately accruing reward tallies, Koechlin and his coauthor Sylvain Charron (of the same institution) found that the subjects' brains divided the two reward-based goals between the two sides of the region. The results were published online April 15 in Science.

The area of the brain that was highly active in the observed multitasking behavior, the frontopolar cortex (which organizes pending goals while the brain completes another task), is "especially well developed" in humans, Koechlin says. It helps organize tasks and the order in which their components should be completed (as highlighted by patients who have damaged this part of the brain and are especially poor at multitasking, he notes). This area's lesser development in other primate species leads Koechlin to think that the ability to hold more than one goal in mind at once might be unique to our species.

The new work does not, however, show that the brain can actually execute two distinct tasks, such as letter matching, at precisely the same time, Paul Dux a psychology lecturer at the University of Queensland in St. Lucia, Australia, noted in an email to ScientificAmerican.com. The data reveal that though separate goals might be running concurrently in the brain, "there are still large dual-task costs" when people have to switch between two tasks making for "non-efficient multitasking," cautioned Dux, who was not involved in the new research but has also studied attention in the brain. (Some commonplace activities, such as driving and talking on a cell phone frequently go hand-in-hand, but the brain is likely switching its main focus quickly between the two activities, perhaps a reason the pairing has been so dangerous.)

Although the letter-matching tasks were simple, Koechlin says that the same hemisphere split would also likely be observed in subjects performing more complex tasks. "Task complexity itself does not prevent from dual-tasking," he explains. "People should be able to switch back and forth between two complex tasks (by postponing one while executing the other one), provided that the incentive of pursuing each task is large enough." If one of the tasks sparks too many unrelated thoughts, however, "your frontal lobes should lose track of one task," he notes (perhaps providing more evidence for the hazards of distracted driving).

Within the results of Koechlin's work is an explanation for why people tend to prefer binary options, such as yes-or-no questions and if-then statements. "This finding further suggests that the frontal function cannot keep track of more than two goals/tasks at the same time," Koechlin explains. "Humans have problems deciding between more than two alternatives…. A possible explanation is that they cannot keep in mind and switch back and forth between three or more alternatives."

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